Test system and method for testing high-voltage technology

ABSTRACT

The present invention relates to a test system for high-voltage technology devices, in particular shunt reactors, as defined in the preamble of independent patent claim  1.  The invention also relates to a method which can be carried out with this test system and is intended to test high-voltage technology devices according to coordinate patent claim  5.  The general idea of the test system according to the invention is to provide a continuously adjustable inductance and a capacitance, which can be adjusted in in discrete steps, on the secondary side of the test transformer in such a manner that said components form a series resonant circuit together with the test object in the form of an inductance. In the method which can be carried out with the test system according to the invention, a rough adjustment of the test system is carried out using the discretely adjustable capacitances of the capacitor bank by connecting individual capacitances of the capacitor bank via an iterative process if an undercapacitance is measured in the test system by means of a measuring device or by disconnecting individual capacitances if an overcapacitance is measured by means of the measuring device until a predefined threshold value of an overcapacitance prevails, with the result that fine tuning of the test system is then carried out by means of the continuously adjustable inductance in such a manner that said components form, together with the test object in the form of an inductance, a series resonant circuit which can be tuned to the point of resonance thereof.

The present invention relates to a test system for apparatus from thehigh-voltage field, particularly shunt reactors, as defined in thepreamble of independent claim 1. The invention further relates to amethod, which can be performed by this test system, for testingapparatus from the high-voltage field in accordance with parallel claim5.

Shunt reactors, also known as compensation choke coils, are sufficientlyfamiliar to the expert from the prior art and are in that case focusedon medium-voltage and high-voltage mains for improvement of stabilityand economy of energy transmission systems. They essentially comprise acoil with at least one winding and an iron core, which is displaceablebetween the windings of the coil, for controlling inductance. Theseapparatus from energy technology provide compensation for the capacitivereactive powers of transmission lines, particularly in lightly loaded oridle running transmission mains. Shunt reactors reduce mains-frequencyover-voltages in the case of sudden drop in load or transmission mainsin idle running. In a test system for apparatus from the high-voltagefield a compensation choke coil represents an inductance to be checked.

The high-voltage test checks whether the compensation choke coil wascorrectly produced in terms of quality. In that case, a so-called surgevoltage check has in principle the purpose of simulating transientover-voltages in three-phase mains by means of artificially generatedpulse-like surges. A substantially more wide-ranging area is representedby tests with alternating voltage. The test object is in that case actedon by an alternating voltage. In this way it is possible, for example,to check the linearity of the compensation choke coil, its vibration andnoise behavior, or temperature coefficients. Further significantelements are loss- power measurement and induced voltage testing bypartial discharge measurement. The last-mentioned test delivers adecisive statement about the quality of the high-voltage insulation ofthe compensation choke coil.

The requirements, forms of voltage and determination of the parametersthereof are defined in IEC 60060-1, IEC 60076-3 and IEC 60076-6.

A test system, which is known from the prior art, for shunt reactorssuch as defined by the preamble of the applicable main claim is shown inFIG. 1. This test system is particularly suitable for testing shuntreactors and comprises a motor-generator set electrically supplied by asupply source. Within the test system, the motor-generator set has thetask within the test system of adapting and regulating the frequency andvoltage for the test system. As an alternative to the motor-generatorset it is also possible to provide a frequency converter connected bythe inputs thereof with an energy source, for example the power mains.The outputs of the motor-generator set or alternatively of the frequencyconverter are in that case connected with the primary side of a testtransformer. A compensation unit, here a variable capacitor, isinterposed in the connecting line between the outputs of themotor-generator set or of the frequency converter. The actual testobject, namely the shunt reactor, which in its electrically equivalentcircuit diagram represents an inductance, is connected with thesecondary side of the test transformer. In order to reduce the voltageat the test object to measurable values, provided between the testobject and the secondary side of the test transformer is a voltagedivider that is connected with an evaluating unit (not illustrated). Allthese mentioned components of a test system, which is known from theprior art, for shunt reactors have been known to the relevant expert fordecades and, for example, available from the applicant as a test systemfor apparatus from the high-voltage field.

In order to be able to test shunt reactors of very high power of, forexample, 110 MVA or thereabove it is necessary in the case of the testsystem known from the prior art to provide a test transformer withequally large electrical parameters, since the test transformer has tobe designed for the maximum test voltage. The motor-generator set, whichtogether with the energy source is constructed for electrical powersupply of the test transformer, similarly has to be designed for themaximum test voltage. The costs of the test system are essentiallydetermined by the electrical dimensioning of the test transformer. Atest transformer designed in that way with an electrical power of up to110 MVA in that case costs some millions of euros and in addition due toits mass is no longer movable by cranes.

The object of the present invention is therefore to provide a testsystem for apparatus from the high-voltage field in which the testtransformer in terms of its electrical parameters no longer has to bedesigned for the maximum test voltage to at most be applied to the testobject. Moreover, it is an object of the invention to indicate a methodthat can be performed by this test system.

This object is fulfilled by a test system for apparatus from thehigh-voltage field, particularly shunt reactors, with the features ofthe first patent claim as well as by a method with the features of theparallel, fifth patent claim.

The general idea of the test system according to the invention consistsof providing a continuously adjustable inductor as well as a capacitoradjustable in discrete steps on the secondary side of the testtransformer in such a manner that the stated components together withthe test object, which forms an inductor, form a series resonant circuitthat is tunable to its point of resonance. The essential components ofthe test system are in that case the actual test object, namely theshunt reactor forming an inductor, as well as the capacitor bankrepresenting a capacitor. These two components as well as the adjustableinductor, which can be constructed as, for example, an adjustable choke,form in accordance with the essence of the invention in their mutualinteraction a series resonance circuit supplied by an energy source anda motor-generator set. In order to tune the test system to the point ofresonance the capacitor, which is adjustable in discrete steps, of thecapacitive bank, the test object forming an inductor and the inductor,which is adjustable in continuous steps, of the adjustable choke aretuned to one another, which takes place in accordance with the steps ofthe method according to the invention described in the following. Thus,the test transformer previously matched in its electrical parameters tothe test object can be constructed to be significantly smaller and moreeconomic. In accordance with the essence of the invention a testtransformer with a power of only 4 MVA is sufficient for a shunt reactorof 110 MVA. Not only can the test transformer be thus dimensioned forsmaller powers, but also the motor-generator set for supply of the testsystem, which previously had to provide the entire power imposed on thetest system, can be adapted to the outline parameters varying inaccordance with the invention. The overall costs for the test system arethus significantly reduced by comparison with the prior art.

In order to be able to propose a method performable by the test systemaccording to the invention the following technical problem wouldadditionally have to be solved: the electrical parameters of the testobject, particularly the inductance thereof, are in that case invariableand form a constant within the test system. At the same time, in thecase of the electrical parameters of the test object it is necessary totake into account, due to production tolerances, a departure of up to 5%from target values, so that the outline parameters of the test systemcannot be readily provided in advance and thus preset. The frequencyconverter of the test system can in that case produce variablefrequencies of up to 200 Hz, in which case two frequencies are ofimportance for the test:

-   -   induced voltage test with a frequency of 120 to 200    -   loss-power measurement at mains frequency, i.e. 50 or 60 Hz

In the case of the induced voltage test an additional fine tuning of theresonant circuit of the test system according to the invention by way ofadaptation of the test frequency adjustable by the frequency convertercan be carried out, since the test frequency, as mentioned above, may befreely selected within a defined bandwidth. However, in the case of theloss-power measurement a fixed test frequency is stipulated by therelevant IEC. Here, a precise matching between capacitance andinductance is required. Since the capacitor of the capacitor bank, assimilarly mentioned above, can be adjusted only in discrete steps, i.e.not continuously, in accordance with the invention an additionaladjustable choke for fine tuning of the test circuit is provided. Thisis because, as a counter-move, the inductor thereof is adjustablecontinuously over a specific range. However, this continuouslyadjustable range is relatively small and does not balance out theproduction tolerances of the electrical parameters of the test object ofup to 5%.

A method able to be performed by the test system according to theinvention is therefore proposed in which by way of the discretelyadjustable capacitors of the capacitor bank a coarse adjustment of thetest system is carried out in that by means of an iterative processindividual capacitors of the capacitor bank are switched on when abelow-threshold capacitance is measured in the test system by means ofmeasuring device and individual capacitors are switched off when anabove-threshold capacitance is measured by means of the measuringdevice, until a previously fixed threshold value of an above-thresholdcapacitance prevails, so that fine tuning of the test system issubsequently carried out by means of the continuously adjustableinductor in such a way that the stated components together with the testobject forming an inductor form a series resonant circuit tunable to itspoint of resonance.

The invention will be explained in more detail in the following by wayof example on the basis of drawings, in which:

FIG. 1 shows a test system, which is known from the prior art, forapparatus from the high-voltage field, as acknowledged in theintroduction to the description, and

FIG. 2 shows a test system according to the invention for apparatus fromthe high-voltage field.

A test system according to the invention for apparatus from thehigh-voltage field, particularly those representing an inductance in theelectrical equivalent circuit diagram thereof, is shown in FIG. 2. Thetest system comprises an energy source 8 for electrical power supply,wherein the energy source 8 can be formed by, for example, the powermains present anyway. In FIG. 2 the energy source 8 is connected withinputs of a frequency converter 9 that can be constructed as aconventional proprietary frequency converter. Instead of energy supplyat the power mains side in interaction with a frequency converter 9 thetest system according to the invention can alternatively also beoperated by a motor-generator set 10. The motor-generator set 10 haswithin the test system the task of adapting and regulating frequency andvoltage for the test system. The motor-generator set 10 thus representsan equivalent, which is known to the expert, to the frequency converter9. The outputs of the frequency converter 9 or of the motor-generatorset are in that case connected with a primary side 11.1 of a testtransformer 11. The electrical input variables of the test transformer11 are, depending on the respective embodiment, 5 kV-20 kV, 50 Hz forloss-power testing or 200 Hz for induced voltage testing. The embodimentof the motor-generator set 10 is oriented toward the local conditions ofthe energy supply, which leads to a multiplicity of variants. The testfield is frequently supplied by an industrial energy supply mains(three-phase alternating voltage, 50 Hz, 10 kV-20 kV). In this case themotor is constructed as an electrical machine, preferably as asynchronous machine. If a high-power electrical energy supply mains isnot present, then use can be made instead of a diesel motor in order tothus replace the energy source. The motor together with a generator isseated on a common shaft. The kinetic energy is converted in thegenerator into an electrical energy and delivered to the testtransformer 11. In the most frequent cases the generator is asynchronous machine. The exact form of embodiment, i.e. salient polemachine or non-salient pole machine, pole pair number, is orientedtoward the rotational speed of the connected shaft and thus to theembodiment of the motor.

A test object 12, namely a shunt reactor, which represents an inductancein its electrical equivalent circuit diagram, is connected with asecondary side 11.2 of the test transformer 11. In departure from theprior art, which is illustrated in FIG. 1, the test system according tothe invention has on the secondary side 11.2 of the test transformer 11a continuously adjustable inductor 13 as well as a capacitor 14adjustable in discrete steps, the two of which are integrated as aseries circuit in the test system in such a manner that a seriesresonant circuit can be formed by the mentioned components together withthe test object 12 forming an inductor.

In order to reduce the voltage of the test object 12 to measurablevalues a voltage divider connected with an evaluator unit (notillustrated) is provided between the test object 12 and the secondaryside 11.2 of the test transformer 11.

In the case of the method able to be performed by the test systemaccording to the invention a coarse adjustment of the test system iseffected by way of the discretely adjustable capacitors 14 of thecapacitor bank in that individual capacitors 14 of the capacitor bankare switched on by way of an iterative process when a below-thresholdcapacitance in the test system is measured by means of a test device orindividual capacitors are switched off when an above-thresholdcapacitance is measured by means of the measuring device, until apreviously fixed threshold value of an above-threshold capacitanceprevails, so that subsequently by means of the continuously adjustableinductor 13 a fine tuning of the test system is carried out in such amanner that the mentioned components together with the test object 12,which forms an inductor, form a series resonant circuit that can betuned to the resonance point thereof.

Reference Numeral List

1 motor-generator set

2 energy source

3 frequency converter

4 test transformer

4.1 primary side

4.2 secondary side

5 variable capacitor

6 test object (inductor)

7 voltage divider

8 energy source

9 frequency converter

10 motor-generator set

11 test transformer

11.1 primary side

11.2 secondary side

12 test object

13 adjustable inductor

14 adjustable capacitor

15 voltage divider

1. A test system for an apparatus from the high-voltage field constituting a test object, the test system having: an energy source for electrical supply of the test system, a motor-generator set electrically connected with the energy source for adaptation and regulation of frequency and voltage within the test system, and a test transformer is having a primary side electrically connected by with the motor-generator set and a secondary side electrically connected with the actual test object, the test system comprising: a continuously adjustable inductor and a capacitor adjustable in discrete steps on the secondary side of the test transformer so that the continuously adjustable inductor as well as the capacitor adjustable in discrete steps form together with the test object a series resonant circuit that can be tuned to the a point of resonance thereof.
 2. The test system according to claim 1, wherein the continuously adjustable inductor is an adjustable choke.
 3. The test system according to claim 1, wherein the capacitor adjustable in discrete steps is a capacitor bank.
 4. The test system according to claim 1, further comprising: a voltage divider between the secondary side of the test transformer and the test object.
 5. A method of testing apparatus from the high-voltage field constituting a test object by a test system having: an energy source for electrical supply of the test system, a motor-generator set electrically connected with the energy source for adaptation and regulation of frequency and voltage within the test system, and a test transformer having a primary side to electrically connected by the primary side thereof with the motor-generator set and a secondary side electrically connected with the actual test object, and the test transformer transforming the electrical energy of the motor-generator set into a test voltage, the method comprising the steps of: coarsely adjusting the test system by the capacitors adjustable in discrete steps in that individual capacitors are switched on by way of an iterative process when a below-threshold capacitance in the test system is measured by means of a measuring device or individual capacitors are switched off when an above-threshold capacitance is measured by means of the measuring device, until a previously fixed threshold value of an above-threshold capacitance prevails, and subsequently a fine tuning of the test system out by means of the continuously adjustable inductor in such a manner that the capacitor adjustable in discrete steps and the continuously adjustable inductor together with the test object constructed as an inductor form a series resonant circuit that is tuned to the a point of resonance thereof. 